The Wombat board is designed for makers who want to experiment and try out ideas for devices and projects that connect to the Raspberry Pi. It's all about prototyping - taking an idea and seeing where it takes you.
Sure, there are a lot of ready-made Raspberry Pi add-on boards, but what if, like me, you enjoy building your own circuits? Or perhaps the available add-ons don't do quite what you need.
I designed the Wombat board to provide useful facilities, such as:
- clearly labelled and easily accessible GPIO pins
- a solderless breadboard that doesn't limit you to small, simple projects
- pushbuttons and LEDs
that I personally find helpful when starting a design or playing around with ideas.
I also added some features that I wished the Raspberry Pi had, such as:
- analog inputs
- a beefier 3.3 V power supply (the stock 50 mA isn't much...)
- being able to use a micro USB socket to communicate with the Pi's serial port, instead of only using it for power (as the Pi does)
It works with the newer Raspberry Pi models which include a 40-pin GPIO header, such as the A+, B+, and the new Raspberry Pi 2.
It is supplied fully built and comes with a 40-pin IDC cable to connect it to your Raspberry Pi. A comprehensive manual, including schematics, and example Python code will be available for download from www.gooligum.com.au.
- All 40 Raspberry Pi (2, A+ or B+) GPIO pins broken out to a clearly labelled and easily accessible 40-pin header
- Onboard 3.3 V voltage regulator, supplying up to 500 mA to your circuit
- 8 x 10-bit analog inputs, via an analog-to-digital converter (MCP3008) connected to the Raspberry Pi's SPI bus
- All signals conveniently made available alongside a large solderless breadboard, for convenient custom circuit development
- 2 x pushbuttons to use as digital inputs
- 4 x LEDs to use as digital outputs
- 1 x potentiometer to use as a basic analog input
- All onboard I/O devices are clearly labelled with both "BCM" and "Board" numbering schemes
- USB to serial bridge (genuine FTDI FT232), connecting the Raspberry Pi's serial pins to a standard micro USB port
- Able to power the Raspberry Pi via the console USB port - just one standard micro USB cable providing power and connectivity!
- All onboard devices can be disconnected or disabled via jumpers - if you don't need a facility, simply take it out of circuit
$7000 (goal reached!) - add a photocell and temperature sensor, plus an RGB LED (+ resistors) and a set of breadboard jumper wires, along with small projects / example code demonstrating how to use the Wombat board's analog inputs to, for example, smoothly control the color of an LED.
During the Kickstarter campaign, I'll finalise the test process that the manufacturer will use to ensure that every Wombat board is working ok - see this blog entry for some insight into what's gone into getting this so far. I'll also write the manual.
In early April I'll be making a trip to China where I'll meet with the manufacturer, show them the prototypes and and run them through the test procedure, to ensure that they get it right. I'll also be meeting with the company I'll be using for shipping, to make sure that everything is ready to go.
Assuming this campaign is funded (please support it!), manufacturing will kick off and be complete within four weeks. They'll build a couple of prototypes first, which I'll need to sign off on before the final production run. Then it will be time to pack everyone's rewards and ship them. Delivery to most parts of the world will typically take two weeks, but to be safe we should assume up to one month.
That has everyone receiving their rewards by mid June, as you can see from the chart.
I started with a prototype built on a generic protoboard:
Pretty clunky, built with all through-hole components, but it proved the concept and was immediately useful.
I'd brought the RPI's serial pins out to the pin headers you can see at the top right, for connection to a USB-serial cable. I had a cheap one of those cables lying around, but it was difficult to find working Windows 8 drivers for it. And then I realised - the RPi uses a micro USB socket for power. Wouldn't it be great if there was a micro USB socket that could be used, not only for power, but to communicate with the RPi's serial console as well? It's such a useful thing to be able to do (I often go to meetings where I don't have a screen and keyboard for the RPi, and yet I don't necessarily know what IP address my RPI has been assigned, so I need a way to connect in order to find the IP address and maybe configure WiFi) that it's a pity that that facility hadn't been built into the Pi. And yet I could add it to what I was later to call the Wombat board, by adding a USB-serial bridge chip. I went with the FTDI FT232 because it's very well supported by every major operating system, so no more driver issues. And although the genuine FTDI chips are relatively expensive, after the recent FTDI "bricking" Windows driver update controversy, I'm glad I went with the real thing. It just works - well worth the cost.
Around this time it became clear that 40-pin GPIO is the future for Raspberry Pi - first the B+, then A+ and most recently the RPi 2. So when I designed a printed circuit board (PCB), I designed for the new 40-pin standard.
I had some PCBs made and hand-soldered a couple of prototypes (went surface mount to keep the size down, and this is after all the 2010's - although the micro USB socket was quite a challenge to solder by hand!), and they worked fine. These are the boards featured in the video and in the photo above.
I realised that I'd left out one resistor (had to be added under the board, on the prototypes), so the final revision, which will be sent for manufacturing, will be very slightly different to the prototypes.
Risks and challenges
As mentioned under "History" above, the design has been well tested with only one minor change needed for the production version (this change being tested on the prototype), so there is little risk associated with the design.
There are always risks associated with manufacturing - mainly parts availability, schedule and quality.
The risk of parts not being available is very small, because the Wombat board doesn't use any exotic or hard to obtain parts.
I've used the manufacturer I'll be working with for my PIC training board (take a look at http://www.gooligum.com.au/train-dev-boards/base-mid-train-board and you'll see a family resemblance to the Wombat board), which I've been selling for a few years - I'm very pleased with their quality and have a great working relationship with them. Based on this experience, I'm sure that the manufacturing time won't go beyond one month.
I'll ensure quality in the final product by inspecting and testing the first prototypes myself, and in getting the manufacturer to thoroughly test every board before they ship it. And as mentioned, they have done high quality work for me in the past.
Finally, the fulfillment service that I intend to use for packing and shipping the rewards is well regarded, but nevertheless to minimise any potential shipping-related risks, I intend to meet with them and inspect their facility before going ahead.
- (30 days)